– Ed

Eye care needs can more or less be divided into two age groups. Under forty and over forty or, pre-presbyopic and presbyopic. From the age of forty onwards, the focusing mechanism of our eyes starts to deteriorate and what this means, is that we require different strengths of lenses for distance vision and near vision. When we fixate close-up, the lenses in our eyes, at lighting speed, change shape and give us more focusing power to obtain clear vision at near. It is this focusing power that we begin to lose because the lenses start to lose their elasticity. This a normal aging process.

Under forty group

There are several reasons to motivate additional glasses in this group, sporting activities being the most obvious one. Polaroid lenses, which cut out glare off horizontal surfaces such as water, can bring about amazing results in all water related activities. It not only eliminates glare, but it also allows the angler to see into the water. However, polaroid lenses will wreak havoc on digital devices. There are specialised lenses for driving, night driving, cycling, hunting to name a few. For many high risk activities, lenses and frames are designed to prevent ocular injuries. Another, big motivation would be fashion. Optometrists globally, are constantly bemoaning the fact that someone will own many pairs of expensive shoes but only one pair of glasses or drive a Porsche but insist on making do with one cheap pair of glasses.

Over forty group

Here the need for multiple pairs becomes much more functionally driven and prescription related. It has everything to do with working or focusing distance and the ramifications of this are often not clearly understood. Bear in mind, the over forties, require different lens powers for distance and near. Even when one has perfect vision for distance but the near vision goes, it should still be seen as two different powers required although the distance power will be zero strength. It is worth pointing out that, short sighted people (myopes), by removing their spectacles, effectively introduce a different plus power which will enable them to see close up. The common declaration; “My eyes are perfect, I just need readers” is very far from the mark and will hopefully be better understood after reading this piece.

A quick word on how the prescriptions work: the optometrist will determine the lens power required for best vision at six meters and beyond. This could mean a correction for shortsightedness (myopia), farsightedness (hyperopia) or astigmatism on its own or in a combination with the previous mentioned two conditions. With the best distance correction in place, the optometrist will then add a lens power, called the reading addition, to get the best vision at a particular distance at near. For example, a person of age sixty, will have no focusing ability left and at 40cm will require a reading addition of +2,50 diopters. If our patient wants to see clearly and comfortably on a computer screen at 50 cms away, the reading addition will have to be +2,00 diopters.

The take-home message is: to enjoy optimal clear and comfortable vision, the lenses will have to be set up for a particular distance, even in the design of bifocals or multifocal lenses. Thus, one pair of spectacles can never fulfill all visual requirements perfectly, simply because nobody ever only operates at one distance.

It is also important to note that your lenses can be positioned in a way that will best suit a particular function. For example, an executive’s multi focals are set up to give him the best vision at his desk and generally in the office. However, this set-up will be far from optimal on the golf course. Here the reading section needs to be lower to provide the best functional vision when addressing the golf ball. By the same token, these office glasses are not going to do well when he is prancing around on the rocks when fishing. Likewise, the female executive’s office glasses are not going to be ideal when she indulges in her favourate past time of crocheting, because she is holding her stuff at 13cms where it is most comfortable physically.

A reading prescription, because it is set up for near, will be blurred when looking into the distance. That’s why we revert to multifocals and bifocals. But, be sure, the best option for reading in bed is plain old readers.

Computers present their own visual demands. Here, in multi focal form, the top part is best set for optimum vision at say 60 cms and the reading part for 40 cms. This provides a much better range of clear vision from the normal reading distance to the computer screen and it will suit several other activities with similar visual demands, such as looking at maps or building plans.

To illustrate why one pair can never fulfil all visual functions, here are some examples of visual tasks that can’t be covered by the same spectacle prescription:


Visiting the optometrist, it will be worthwhile making a list of all activities important in your life. Bear in mind that the optimal visual correction is directly related to the working distance of that activity. For example, it would be valuable to the optometrist to have a measurement of how far the sheet music is from a violinist. Moreover, the way that the spectacles are set up, will relate to how functional they are for a particular task. It’s all about the working distance.

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